The present invention relates to a hermetic rotary compressor, and more particularly to a compressor which is suitable for high-speed operation.
As shown in FIG. 5, a conventional hermetic rotary compressor includes a motor unit 3 composed of a rotor 1 which normally rotates in the direction of an arrow A and a stator 2 is arranged in an upper portion of a hermetic housing 10. In a lower portion of the hermetic housing 10 is disposed a compressor unit 8 comprising a cylinder 4, a roller 5, a main bearing 6, a lower bearing 7 and a partition board (not shown). The motor unit 3 and the compressor unit 8 are connected by a crank shaft 9. Lubricating oil 11 is stored at the bottom portion of the hermetic housing 10, and this oil lubricates each sliding portion of the compressor unit 8 via an oil supplying path (not shown) formed inside the compressor unit 8. The roller 5 is fitted to a crank portion 9a of the crank shaft 9 so as to freely rotate, and this roller 5 rotates eccentrically within the cylinder 4 so that a refrigerant is sucked and compressed. The compressed refrigerant is passed through a valve 12 and then discharged out to a discharging silencer 14 formed by a valve cover 13 and the lower bearing 7. The compressed refrigerant is then passed through a discharging path (not shown) and flows out to a space 10a within the hermetic housing 10. In operation of this compressor, centrifugal force is generated to act on the above-mentioned crank portion 9a and roller 5, so that there is a possibility that the crank shaft 9 is deflected during rotation at the portion carrying the crank portion 9a and the roller 5. To obviate this problem, first and second rotor balance weights 15 and 16 are normally provided on upper and lower edges of end ring of the rotor 1, and the centrifugal force acting on the crank portion 9a and roller 5 is cancelled by the centrifugal force generated by these first and second rotor balance weights so as to balance the crank shaft 9. Theoretically, the conditions for the balance of the crankshaft are expressed by the following formulae. EQU Fo+Fb-Fa=O, and EQU Fa.multidot.La-Fb.multidot.Lb=O.
From there formulae, the following formulae are derived. EQU Fa=Fo.multidot.Lb/(Lb-La), and EQU Fb=Fo.multidot.La/(Lb-La),
where Fo represents the centrifugal force acting on the crank portion 9a and roller 5, Fa represents the centrifugal force on the rotor balance weight 16, and Fb represents the centrifugal force on the rotor balance weight 15. The distance between the crank portion 9a and the rotor balance weight 16, and the distance between the crank portion 9a and the rotor balance weight 15 are represented by La and Lb, respectively. More specifically, since each of the denonimators of the centrifugal forces Fa and Fb is expressed by difference form, i.e., (Lb-La), there is a tendency that the centrifugal forces Fa and Fb increase, so that the masses of the rotor balance weights 15 and 16 must be increased. Consequently, load applied to the crank shaft 9 is increased, so that a problem is encountered in that it is difficult to efficiently utilize the electric energy given to the electric motor unit 3.
In order to solve this problem of the conventional compressor, a compressor has been proposed in Japanese Examined Patent Publication No. 61-45079 is proposed and is shown in FIG. 6.
In the compressor shown in FIG. 6, in order to cancel centrifugal force Fo1, a lower balance weight 17 is attached to the end 9b of the crank shaft 9 adjacent to a lower bearing side edge portion 9b of the crank shaft 9, while a rotor balance weight 15 is provided on the upper end portion of the rotor 1. The conditions for the balance are theoretically expressed as follows. EQU Fa1+Fb1-Fo1=O, and EQU Fa1.multidot.La1-Fb1.multidot.Lb1=O.
Therefore, the following formulae can be obtained. EQU Fa1=Fo1.multidot.Lb1/(Lb1+La1), and EQU Fb1=Fo1.multidot.La1/(Lb1+La1),
where, Fo1 represents the centrifugal force acting on the crank portion 9a and roller 5, Fa1 represents the centrifugal force of the lower balance weight 17, and Fb1 represents the centrifugal force of the rotor balance weight 15. The distance between the crank portion 9a and lower balance weight 17, and the distance between the crank portion 9a and rotor balance weight 15 are represented by La, and Lb, respectively. More specifically, each of the denominators of the centrifugal forces Fa1 and Fb1 is expressed in a sum form, i.e., (Lb1+La1), unlike the construction of FIG. 5 which employs the difference form (Lb-La). Therefore, compared to the construction of FIG. 5, the values of centrifugal forces Fa1 and Fb1 are remarkably reduced. It is therefore possible to decrease the masses of lower balance weight 17 and rotor balance weight 15, so that the load of bearing can be remarkably reduced.
However, since the length of crank shaft 9 between the compressor unit 8 and the motor unit 3 is considerably large, there is a possibility in that large deflection of the crank shaft 9 is generated at the side of rotor balance weight 15 as the speed of rotation in the direction A becomes higher.
In addition, in the conventional arrangement shown in FIG. 6, the lower balance weight 17 is surrounded by a cover body 18 which plays both a role of a valve cover and a role of a balancer cover so as to prevent the lower balance weight 17 from unnecessarily stirring the lubricating oil 11. Since the cover body 18 acts both as the valve cover and balancer cover, the interior of the cover body 18 is filled with the discharged gas so as to enable the lower balance weight 17 to rotate without stirring the lubricating oil.
The cover body 18 capable of functioning both as the valve cover and balancer cover in the abovementioned proposed prior art, however, poses the following problems when this prior art is actually embodied in the compressor.
More specifically, since the lower balance weight 17 is arranged within a chamber 19 constituting the discharging silencer, when the liquid refrigerant or the gas-liquid mixture of the refrigerant is discharged from the valve 12 into the silencer chamber 19 particularly in the start-up or in so-called liquid back operation, the lower balance weight 17 must stir such fluid so that vigorous foaming phenomenon is caused by the mixing effect. Then, the foam or bubbles of refrigerant fills up the space 10a in the hermetic housing 10, so that there is a possibility that the rotation load is abnormally increased and the input current to the motor 3 is correspondingly increased, or an excessive amount of lubricating oil is discharged out of an discharge port 10d of the hermetic housing 10 so that the oil surface level is lowered.
As stated before, the cover body 18 functions both as the valve cover and as the balancer cover, while the crank shaft 9 shown in FIG. 6 is a movable element. Hence, it is necessary to provide a minimum gap between the lower end portion 9b of crank shaft 9 and a ring portion 18a of the cover body 18 to which this lower shaft end portion 9b is fitted, in order to enable assembly of the compressor.
Consequently, there is fear that the noise leaks through the gap to result in the increase of the noise from the compressor. It would be possible to eliminate the gap by inserting a seal member such as packing and 0-ring into the gap. In such a construction, the crank shaft and seal member are frictioned by each other with the results being that the rotation load increases and durability of the seal member is impaired to disable the seal member to stand a long use.
An object of the present invention is to provide a compressor in which the problem encountered when the balance weight is provided at lower shaft end portion of the crank shaft is reduced.
To these ends, according to one aspect of the present invention, there is provided a hermetic rotary compressor having a motor unit composed of a stator and a rotor which are arranged in an upper portion of a hermetic housing, an oil-lubricated compressor unit arranged in a lower portion of the hermetic housing, a crank shaft connecting the motor unit and the compressor unit, and a discharge silencer formed by a lower bearing of the compressor unit supporting a lower end portion of the crank shaft and a cover of the lower bearing, wherein the hermetic rotary compressor further comprises a lower balance weight mounted on a lower shaft end portion of the crank shaft which extends to a position below the discharge silencer and two rotor balance weights provided on both end portions of the rotor.
In this hermetic rotary compressor, the lower balance weight provided in addition to the two rotor balance weights provides a three-points balancing construction for the compressor, so that it is possible to reduce the amount of deflection of the crank shaft.
In a preferred embodiment of the present invention, the compressor further comprises a weight cup surrounding the lower balance weight.
In another aspect of the present invention, there is provided a hermetic rotary compressor having a motor unit composed of a stator and a rotor which are arranged in an upper portion of a hermetic housing, an oil-lubricated compressor unit arranged at a lower portion of the hermetic housing, a crank shaft connecting the motor unit and the compressor unit, and a discharge silencer formed by a lower bearing of the compressor unit positioned at a lower end portion of the crank shaft and a cover of the lower bearing, wherein the hermetic rotary compressor further comprises a lower balance weight mounted on a lower shaft end portion of the crank shaft which extends to a position below the discharge silencer and a weight cup surrounding the lower balance weight.
According to the another aspect of the present invention, there is no lower balance weight within the discharge silencer, so that there is no risk of stirring of liquid even when the liquid refrigerant or gas-liquid refrigerant mixture is discharged from the discharging valve of the compressor unit into the silencer in the start-up or liquid-back operation of the compressor.
According to the present invention, the weight cup is preferably provided with an inlet opening which permits the lubricating oil to flow into the weight cup and an outlet opening which permits the lubricating oil to flow out of the weight cup during the operation of the compressor.
It is also preferred that the weight cup has a hollow cylindrical shape having a bottom portion, with the inlet opening formed in the bottom portion of the cylinder, while the outlet opening is formed in side wall portion of the cylinder.
Further, according to the present invention, preferably, a lubricating oil passage is formed in the compressor unit such that the lubricating oil passing through the oil-lubricated compressor unit is relieved from the lower shaft end portion of the crank shaft to a region which is in the vicinity of upper face of the lower balance weight within the weight cup.